This invention relates to development apparatus in electrostatographic copiers and printers, and more particularly to a development apparatus that includes a mechanism for completely and efficiently unloading or purging spent developer material from such apparatus.
In electrostatographic copiers and printers that produce or reproduce copies of images, it is well known to use triboelectrically charged developer material held in a development apparatus, to develop latent images formed electrostatographically on an image-bearing member. The development material may consist, for example, of a mix of carrier particles and toner particles which possess properties allowing them to be triboelectrically charged to opposite polarities respectively by being stirred and mixed together within the development apparatus. When developer material, charged as such, is used to develop electrostatically formed images as above, the charged toner particles are attracted to, and held by the images being developed, while the carrier particles are left in the development apparatus.
The quality of images so developed depends significantly on the charge value, as well as, on the concentration of toner particles in the developer material mix. Image development, of course, gradually depletes the level or concentration of toner particles in the developer material mix within the development of images, the concentration of toner particles in the mix is monitored, and is controlled by periodically replenishing or adding fresh toner particles to the spent mix within the development apparatus. Additionally, image development also gradually depletes the quantity of carrier particles within the development apparatus through some of the carrier particles being undesirably picked up by the image-bearing member during development.
More significantly too, the rest of the carrier particles left in the development apparatus usually will reach a point where they start to lose their triboelectric properties, thereby detrimentally affecting the charge values of subsequent developer mixes obtained merely by adding fresh toner particles to such carrier particles. Therefore, in order to maintain quality development of images over time, the entire developer mix contents of the development apparatus must at such point be completely unloaded or purged, and the apparatus refilled with fresh carrier and toner particles.
Conventional apparatus and mechanisms for doing so, as disclosed for example in U.S. Pat. No. 4,451,133 issued May 29, 1984, to Kopp et al, typically have included many movable parts such as pivotable plates, flexible tubes and releasable clamps, in addition to damagable parts such as the tubes. Such conventional devices also require separate means for closing or sealing their access opening into the development apparatus. As such, they involve the risk of inadvertent spills from misclosures, as well as, significant downtimes for opening and closing such means.